Ch9 halogens Flashcards
Reactivity trend
Decreases down the group
- gains electrons less easily
atomic radius increases
shielding effect increases
Boiling point trend
Increases down group
- increased number of electrons increases number of London dispersion forces
- require more energy to overcome(decreases volatility)
Fluorine
yellow gas at rtp
most electronegative element
manufactures fluorocarbons
Chlorine
green gas at rtp
used in production of polymers
kills bacteria in drinking water
bleaches paper and textiles
bromine
orange liquid at rtp
used to make products including flame retardants and medicines
iodine
nearly black solid at trp
used in medicines, dyes and catalysts
needed in diet so thyroid gland can make thyroxine(hormone that regulates growth and metabolism)
chemical properties
form -1 halide anions
Basic ionic equation
H2 + 2e- -> 2H-
Displacement experiment
oxidising power decreases down group
Fluorine oxidises Cl-, Br- and I- from solution
Chlorine displaces Br- and I- from solution
Bromine displaces I- from solution
Iodine cannot displace any
bromine is orange-brown
iodine is brown-black but purple/violet when dissolved in hexane
Chlorine + water reaction
Cl2(aq) + H2O(l) <=> HCl(aq) + HClO(aq)
chloric acid molecules pass through cell walls of bacteria
- HClO molecules break up and kill organism by oxidising and chlorinating molecules that make up structure of walls
Benefits of CL2 water treatments
- kills micro-roganisms so greatly reduces risk of water-borne diseases e.g. cholera
Disadvantages of Cl2 water treatment
- can produce harmful by-products
- can react with organic matter in water e.g. producing CHCl3 which can increase risk of bladder cancer
Testing for halide ions
First acidify with dilute nitric acid HNO3
Then add silver nitrate AgNO3(aq)
Can also add ammonia
Chloride halide test
White ppt (silver chloride)
Dissolves in dilute ammonia to give colourless solution
Bromide halide test
Cream ppt (silver bromide)
dissolves in dilute NH3 to give colourless solution
